Filamentary material

ABSTRACT

A MELT SPUN RANDOM OXYMETHYLENE POLYMER FILAMENTARY MATERIAL HAVING AT 70 DEGREES FAHRENHEIT AN ELASTIC RECOVERY OF AT LEAST ABOUT 70 PERCENT FROM AN EXTENSION UP TO ABOUT 50 PERCENT.

May 9, 1972 M. J. COPLAN ET AL 3,661,853

FILAMENTARY MATERIAL Original Filed Jan. 31. 1964 S ecss GPA/GS/Qfzwa? S 55 an/0am Z5 [Pram/cw Panza/yr IN VENTORS MYRON J COPLAN HOWARD I FREEMAN JOSEPH S PANTO United States Patent 3,661,853 FILAMENTARY MATERIAL Myron J. Coplan, 47 Speen St., Natick, Mass. 01760; Howard I. Freeman, 34 Livingston Road, Sharon, Mass. 02067; and Joseph S. Panto, P.0. Box 223, Dover, Mass. 02030 Continuation of application Ser. No. 859,597, Jan. 2, 1969, which is a division of application Ser. No. 341,725, Jan. 31, 1964. This application July 10, 1970, Ser. No. 56,187

Int. Cl. D0111 5/12 US. Cl. 26067 FP 6 Claims ABSTRACT OF THE DISCLOSURE A melt spun random oxymethylene polymer filamentary material having at 70 degrees Fahrenheit an elastic recovery of at least about 70 percent from an extension up to about 50 percent.

This application is a streamline continuation of the now abandoned application Ser. No. 859,597 filed Jan. 2, 1969, which in turn is a divisional application of Ser. No. 341,725 filed Jan. 31, 1964, now abandoned.

This invention relates to the preparation of relatively elastic filaments of an oXymethylene polymer.

It has been proposed to prepare filaments from oxymethylene polymers, e.g., by melt spinning. Such filaments, especially those prepared from oxymethylene copolymers such as the copolymers described in Pat. No. 3,027,352 issued to Walling et al., have many outstanding properties such as high strength, stiffness and stability. We have now discovered an entirely new type of oxymethylene polymer filamentary material which, unlike the filaments of the prior art, possesses a high degree of elasticity after being subjected to a relatively large amount of stretch, e.g. 50% or more at 70 F. These new filaments are particularly useful in the preparation of elastic yarns for stretch garments, either alone or in a blend with a non-elastic material. The new filamentary materials have been found to be superior to known elastic fibers, such as spandex fibers, in such properties as breaking tenacity and stitfness as indicated, for example, by initial modulus.

It is accordingly an object of this invention to prepare a new elastic filamentary material.

It is a further object of this invention to provide an elastic, random, oxymethylene copolymer filamentary ma terial having properties superior to those of known elastic materials.

It is a still further object to provide a process for the production of the above-described elastic filamentary material.

Other objects will be apparent from the following detailed description and claims.

FIGS. 1 to 3 show typical stress-strain curves for filamentary materials of this invention as more fully described hereinafter at up to 50% strain (curve A) as compared with the stress-strain curve of one of the stiifest commercially available spandex yarns (curve B).

In accordance with one aspect of the invention, there is provided filamentary material of an oxymethylene polymer having an elastic recovery at zero recovery time Patented May 9, 1972 (hereinafter defined) at F. of at least about 70% when subjected to a strain, for example, of up to 50%, and preferably an elastic recovery at zero recovery time of at least about when subjected to a strain of 35 to 50%. More specifically, the material has at 70 F. an elastic recovery at zero recovery time of at least about 70%, preferably at least about 75 when subjected to a strain (or extension) of 50%. In particular, filamentary materials having at 70 F. an elastic recovery at zero recovery time of at least about or 90% after being subjected to an extension of 50% are contemplated under the invention.

In general, the elastic recovery after two minutes recovery time of the above-described filamentary material is at least 10% greater than the values of elastic recovery at zero recovery time. Thus, filamentary materials are contemplated under the invention which have an elastic recovery at 70 F. after two minutes recovery time (as hereinafter defined) of at least about 80% When subjected to a strain of up to 50% and preferably an elastic recovery at 70 F. after two minutes recovery time of at least about when subjected to a strain of about 35 to 50%. More specifically, material is contemplated which has an elastic recovery at 70 F. after two minutes recovery time of at least about 80 or 85 eg about 85 to 98%, when subjected to a strain of 50%. In particular, filamentary material having at 70 F. an elastic recovery after two minutes recovery time of about to 100% is included within the invention.

The filamentary material of this invention also has comparatively high elastic recoveries when stretched to extensions substantially higher than 50%. Thus, material is contemplated having at 70 F. an elastic recovery after two minutes recovery time of at least about 70%, e.g., about 72 to from a strain, and at least about 60%, e.g., about 60 to 85% from a strain.

The filamentary material maintains a substantial degree of its elasticity at elevated temperatures. Thus, the filaments may, when subjected to a strain of 50% have elastic recoveries after two minutes recovery time of at least about 70%, e.g., about 75 to 97%, at a temperature of 130 F., at least about 70%, e.g., about 72 to 96% at a temperature of F.; and at least about 60%, e.g., about 62 to 82% at 250 F.

The values for elastic recovery given above are for the first cycle of strain and recovery, using the procedure described hereinafter. It has been found in addition that the elastic recovery of the filamentary material between consecutive cycles changes little, after the material has been subjected to several cycles of strain and recovery. Thus, material is contemplated which, when subjected to seven cycles of 50% strain and recovery, has an elastic recovery at 70 F. with zero recovery time which decreases less than 1.5, and generally less than 1.0 percentage units between the start of the sixth and the start of the seventh cycle.

While various values are given above for elastic recovery after zero and two minutes recovery time, it should be understood that the material of the invention is capable of recovering an additional amount, i.e., may have a still higher elastic recovery, when the recovery time is substantially greater than two minutes.

In addition to these elastic properties the filaments generally have, e.g. at 70 F., a breaking tenacity of at least about 1.0, preferably at least about 1.3, e.g., about 1.3 to

used above 2.5 grams/denier, a breaking elongation of at least about 55%, preferably at least about 7%, e.g., about 75 to 200%, and an initial modulus of at least about 2 grams/ denier, preferably about 5 to 30 grams/denier. Thus the filaments produced under this invention have other good mechanical properties as well as elasticity, e.g., stiffness and strength.

In addition to the above mechanical properties, the filamentary material of the invention generally has a birefringence of at least about 0.03, e.g. from about 0.04 to 0.08, and most often from about 0.05 to 0.07.

A random oxymethylene copolymer as the term is contains recurring oxymethylene, i.e., CH O-, units interspersed with OR-- groups in the main polymer chain Where R is a divalent radical containing at least two carbon atoms directly linked to each other and positioned in the chain between the two valences, with any substituents on said R radical being inert, that is, those which do not include interfering functional groups and which will not induce undesirable reactions, and wherein a major amount of the O'R units exist as single units attached to oxymethylene groups on each side. A random copolymer may thus be distinguished over a block copolymer wherein repeating units of each monomer make up block segments containing little or no units of any other monomer. Thus, in block copolymers containing oxymethylene and other units, substantially all of the other units are attached to like units rather than oxymethylene units on each side. Particularly preferred are random copolymers which contain from 60 to 99.6 mol percent of recurring oxymethylene groups. In a preferred embodiment R may be, for example, an alkylene or substituted alkylene group containing at least two carbon atoms. Examples of preferred polymers include copolymers of trioxane and cyclic ethers containing at least two adjacent carbon atoms such as the copolymers disclosed in US. Patent No. 3,027,352 of Walling et al.

The preferred random oxymethylene copolymers which are treated in accordance with this invention are thermoplastic materials having a melting point of at least 150 C. and are normally millable at a temperature of 200 C. They have a number average molecular weight of at least 10,000. These preferred polymers have a high thermal stability. For example, if the stabilized oxymethylene polymer used in a preferred embodiment of this invention is placed in an open vessel in a circulating air oven at a temperature of 230 C. and its weight loss is measured without removal of the sample from the oven, it will have a thermal degradation rate of less than 1.0 wt. percent/ min. for the first 45 minutes and, in preferred instances, less than 0.1 wt. percent/min. for the same period of time.

The preferred random oxymethylene copolymers which are treated in this invention have an inherent viscosity of at least one (measured at 60 C. in a 0.1 weight percent solution in p-chlorophenol containing 2 weight percent of (-pinene). The preferred copolymers of this invention exhibit remarkable alkaline stability. For example, if the preferred copolymers are refluxed at a temperature of about 142 C.-l45 C. in a 50% solution of sodium hydroxide in water for a period of 45 minutes, the weight of the copolymer will be reduced by less than one percent.

As used in the specification and claims of this application, the term copolymer means polymers having two or more types of monomeric units, including terpolymers and higher polymers. Suitable oxymethylene terpolymers are those having more than two different kinds of monomeric units such as those disclosed in US. patent application Ser. No. 229,715, filed Oct. 10, 1962 by Walter Heinz and Francis B. McAndrew, which application is assigned to the same assignee as the subject application.

In accordance with another aspect of the invention, the filamentary material of this invention is formed by melt spinning a fiber-forming oxymethylene polymer, i.e., extruding the polymer in the form of a melt through the orifices of a spinneret at a shear rate of about 250 to 2500 reciprocal seconds to form filaments which are taken up at a drawdown or spin draw ratio of at least about 25, e.g., up to about 350, preferably about to 235 when the quench temperature in 70 F. The product as spun may have elastic properties as described above, and may be formed into a yarn package, or may be subjected to further treatment as described hereinafter before packaging. In any case, the yarn which is packaged for ultimate use will have the elastic properties described above.

The shear rate of extrusion is defined by the expression 4q/1rr where q is the volume rate of extrusion of the molten polymer through each orifice in cc./sec., and r is the radius of the orifice in centimeters. The shear rate is an indication of the shearing force exerted between the molten polymer of the orifice wall as the polymer is being extruded.

The spin draw or drawdown ratio is the ratio of the velocity of initial yarn take-up to the linear velocity of extrusion of the molten polymer.

In one embodiment of this process, the polymer is melt spun by extrusion through orifices having a diameter for example in the range of about 5 to 25, preferably about 10 to 20 mils, at a linear speed, for example of up to about 15, preferably about 6 to 12 feet/min, at a shear rate within the range set out above, to form filaments which are taken up initially at a speed, for example, in the range of about to 1500, preferably about 450 to 1050 feet per minute, at a drawdown ratio within the ranges set out above. The quench temperature, i.e., the temperature of air or other inert gas such as steam, nitrogen or argon, at the outlet side of the spinneret, is suitably up to about 285 F. A stack or column must be employed downstream of the spinneret if the desired quench temperature is substantially above or below the ambient temperature of air, and may also be useful for better control when air at ambient temperature is used as the quench. However, in the latter case, the polymer may also be extruded directly into air.

In accordance with another aspect of the invention, the as-spun filaments are after-drawn or stretched at a temperature up to about 250 F., e.g., 50 to 250 F., at a draw ratio within the range of about 1.2 to 2.3, preferably about 1.3 to 1.5. The stretching may be carried out by first taking up the yarn on godet rolls from which it is wound on a package and stretching in a separate operation, or in a combined operation, wherein the yarn is initially taken up by one set of godet rolls from which istravels to a second set of godet rolls traveling at a speed faster than the first set so that the cold drawing step is accomplished between the two sets of rolls.

In another embodiment of the process, the freshly spun filaments are passed around a frictional device in the spinning cabinet, e.g., a snubbing pin or pigtail guide which prevents all the tension exerted on the filaments dowstream of the frictional device from being translated back to the face of the spinneret, and the filaments downstream of the frictional device are cold drawn, e.g., by taking up the filaments on godet rolls at a speed greater than that at which they pass around the frictional device. The overall draw ratio between spinneret face and take-up rolls may be for example within the ranges given for drawdown ratio.

While the yarn so produced possesses a considerable degree of elasticity, it is preferable to subject such yarn to a second after-drawing step in amount sufficient to render the fibers uniformly opaque, e.g., at a draw ratio within the ranges given above for the after-drawing step. As is the case when no frictional device is used, the subsequent afterdrawing step may be carried out in a separate operation wherein the yarn from the freshly spun yarn is taken up on godet rolls from which it is wound on a package and is subsequently drawn by conventional means, or as part of a combined operation wherein the yarn from the first take-up godet rolls travel directly to a second set of rolls rotating at a speed greater than that of the first set, with the after-drawing taking place between the rolls.

The initial spinning operation is carried out in a unit which melts the solid polymer and pumps it at a constant rate and under fairly high pressure through the small holes of a spinneret. It is generally desirable to melt spin a polymer having incorporated therein one or more thermal stabilizers. Suitable combinations of stabilizers are shown, for example, in 'French Pat. No. 1,273,219.

Melt spinning temperatures, i.e., of the molten polymer being extruded from the orifices of a spinneret, may range from about 380 to 420 F. for the preferred random oxymethylene copolymers.

The polymer is generally melted by subjecting chips of the polymer to the action of a heated screw extruder. The chips are suitably between about 200 and 2 mesh. The melt is forced through the spinneret orifices by a metering pump. Generally, a filter or sand pack is maintained upstream of the orifices to remove particles or gels which might block them. Preferably, the polymer is maintained as a melt for not more than minutes.

The spinneret may contain, for example, from one to about 500 orifices. Elastic monofilaments, for special uses such as tow rope, may be extruded through orifices up to 100 mils in diameter. The liquid streams emerge from the orifices, generally downwardly, into a gaseous medium, which may be air or an inert gas and solidify.

Filamentary material having the indicated physical properties and also a denier/filament of up to about 20 and even as low as about 1 is contemplated within the invention.

The following examples further illustrate the invention. All properties were measured at 70 F. unless otherwise stated.

EXAMPLE I A copolymer of trioxane and 2 weight percent based on the polymerizable mixture of ethylene oxide was prepared as described in US. Pat. No. 3,027,352 and aftertreated to remove unstable groups as described in Ap plication Serial No. 102,096, filed Apr. 11, 1961. The copolymer was then further stabilized by blending with 0.5 weight percent of 2,2-methylene bis (4-methyl 6- tertiary butyl phenol) and 0.1 weight percent of cyanoguanidine based on the weight of the polymer.

The above-described polymeric compositions was melt spun at 400 F. by means of a gear pump, downward through a 22 hole spinneret having hole diameters of 15 mils and 15 mils in length at a shear rate of about 1140 reciprocal seconds. The resulting 22 filament yarn was taken up by godet rolls at a speed of 1000 feet per minute after passing directly through a pigtail guide located in a column 10 feet long containing air at about 8090 F. A total of 8.17 cc/minute of polymer was extruded through the spinneret, corresponding to a linear speed of 10.68 feet per minute. The drawdown ratio was thus 1000 divided by 10.68 or 93.6.

The yarn obtained by this process was uniformly lustrous but turned opaque on stretching to yield.

The as-spun yarn was lubricated with aqueous polyalkylene glycol-based Ucon H-6N textile finish and was afterstretched in air at room temperature F., using a draw ratio of 2.3 to l.

The properties of yarn obtained, as spun and afterstretched at room temperature, are shown in Table 1.

EXAMPLE II The procedure of Example I was carried out except that the extrusion temperature was 415 F., the spinneret contained 34 holes each, 12 mils in diameter and 18 mils in length, the gear pump was operated so as to obtain an extrusion rate of 4.90 cc./min. corresponding to a linear extrusion speed of 6.48 feet/min, at a shear rate of about 860, the yarn passed over a kiss-roll where it was lubricated with 25% aqueous fatty ester-based Nopcostat 2152-P textile finish, and was then passed through a pigtail guide with one wrap taken around the guide stem. The yarn was then taken up by godet rolls at a speed of 500 feet/min. with an overall drawdown ratio of 77.

The resulting yarn had alternating patches of opaque and lustrous zones with the opaque zones exhibiting a relatively high degree of recoverable stretch.

The patchy yarn was drawn at room temperature (70 F.) at a draw ratio of 2 to l. The resulting yarn was completely opaque, had a total denier of 250, a breaking tenacity of 1.2 grams/denier, a breaking elongation of 160%, and an elastic recovery from 50% extension at A zero recovery time of about The elastic properties of the as spun or after-stretched filamentary material of this invention may be improved by a heat treatment. Preferably the treatment is a hot wet treatment, e.g., contact with hot water or wet steam at a temperature of at least 190 F., e.g. up to about 285 F. for a period of at least one minute.

The following examples illustrate the etfect of a hot wet treatment of the product.

EXAMPLE III-VI TABLE 2 Ex. III, Ex. V, Ex. VI,

ft./min. ftJmin. ftJmin.

Denier 726 219 157 Initial modulus, grams/denier 20. 9 17. 5 23. 2 Tenacity, grams/denier 0. 8 1. 39 1. 74 Breaking elongation, percent 372 195 146 Birefringence, An 0. 0532 0. 0617 0. 0626 Some values of elastic recovery after two minutes recovery time of the four samples of yarn as spun and after a hot wet treatment or boil off i.e., immersion in water under about 15 p.s.i.g. pressure at a temperature of about 250 F. for 30 minutes, were determined after extensions of 50%, 150%, 200% and 250% at temperatures of 70 F., 130 F, F. and 250 F. The results are given in Table 3.

TABLE 3.ELASTIC RECOVERY Temperature of yarn at- 70 F. 130 F. 190 F. 250 F As Boiled As Boiled As Boiled As Boiled Yarn and extension spun off spun ofi spun ofl spun ofl III 250 it. min. ereent: Ex 50 l p 97. 3 73. 96.0 73.6 86. 9 44. 4 62. 6 92. 66. 5 87. 8 34. 1 69. 1 34. 5 41. 5

sz'i iiz 61.2 33.6 "55.8 22.3 30.2 56.4 39.8 60.8 25.4 28.4

97. 6 s9. 2 95. e 74. e 95. 2 e9. 4 71. 2 89.3 71. 6 88. 5 60. 7 s9. 0 44. 7 64. 3 73. 1 51. 7 45. 8 67. 7 49. 3 60. 7 35. 3 56. l 40. 0 29, 30. 4 38. 5

1 At 28 percent. 2 At 185 percent ext. 3 At 125 percent ext.

EXAM PIJE VII spun yarn tapers off rather sharply after a certain stress has been applied (see FIG. 1), whereas this efiect is considerably modified by a dry afterstretching treatment (see FIG. 2). Moreover, a hot wet afterstretching treatment 5 results in a considerable change in the shape of the stressstrain curve, which, after this type of treatment has two points of inflection (see FIG. 3).

The heat treatment, e.g., hot wet treatment described above may be used to improve properties such as elastic recovery of dry afterstretched as well as the as spun yarn. Thus, when the yarn of this example which was dry after- The procedure of Example I was followed except that 30 stretched at 70 F. using a draw ratio of 1.5, was subsethe amount of molten polymer extruded through the spinneret was 4.73 cc./min. at a shear rate of about 660 reciprocal seconds, and the resulting yarn was taken up a speed of 1250 feet/min. resulting in a drawdown ratio of 201. Examples of the yarn were afterstretched at 70 F. in air at draw ratios of 1.2, 1.3, 1.4 and 1.5, and at 170 F. while in contact with a water wet cloth covering a hot metal plate, at draw ratios of 1.2 and 1.4. The physical properties of the yarns obtained are shown in quently immersed in hot water at 250 and 15 p.s.i.g. for a period of 30 minutes, it had the following properties: denier, 126; initial modulus, 29 grams/denier; tenacity, 1.7 grams/denier; breaking elongation, 94%; elastic recovery at zero recovery time after 50% extension, 92%. It can be seen therefore that a hot wet treatment of afterstretched yarn resulted in a substantial increase in initial modulus and elastic recovery.

When the hot wet treated yarn described in the previous Table 4 paragraph was subjected to seven cycles of exten- TABLE 4 Draw ratio At At 170".

As Property spun 1. 2 1. 3 1. 4 1. 5 1. 2 1. 4

Denier 126 122 128 130 110 Initial modulus, grams/denier 26.9 25.6 25.4 15.3 12.5 20 11 Tenacity, grams/denier 1.45 1.35 1. 53 1.45 1. 59 1. 71 1. 98 Breaking elongation, percent 105 110 109 104 104 106 91 Elastic recovery from 50% extension at zero reeoverey time, percent Birefringence, An..

FIGS. 1, 2 and 3 show stress-strain curves (curve A) obtained up to 50% extension, for the yarns of this example as spun (FIG. 1), afterstretched at 70 F. using a draw ratio of 1.5 (FIG. 2), and afterstretched wet at F. using a draw ratio of 1.4 (FIG. 3). In each case, curve B represents a similar stress-strain curve obtained for the stitfest commercial spandex. It can be seen that the yarn included within the invention is in each case considerably stiffer than the spandex, regardless of the aftertreatment. However, the aftertreatment, e.g., afterstretching whether dry or wet and using any of various draw ratios, results in yarns having different stress-strain characteristics which may be utilized in various applica- EXAMPLE VIII The procedure of Example I was followed except that the amount of polymer extruded was 3.26 cc./min. at a shear rate of about 450 reciprocal seconds, the temperature of polymer being extruded was 405 F. and the yarn was taken up at a speed of 1000 meters/min. and a drawdown ratio of 234. Samples of the yarn were afterstretched in air at 70 F. using various draw ratios. Properties of the resulting yarn samples are given in Table 5. In determining the elastic recovery of the yarn, each sample was tions. Thus, the slope of the stress-strain curve of the as 75 subjected to seven cycles of 50% extension at 70 F. and

the elastic recovery at zero recovery time was measured at the end of the first cycle and the end of the sixth cycle.

TABLE Draw ratio Property spun 1.2 1.3 1.4 1.5

Denier 114 107 94 93 101 Initial modulus, grams/denier... 24. 5 18. 7 l5. 3 10.8 8. 0 Tenacity, grams/denier 1. 49 1. 47 1. 59 1. 72 1. 73 Breaking elongation, percent- 129 98 98 89 88 Elastic recovery:

1st cycle, percent 76. 4 78. 8 78. 8 81. 6 75. 2

6th cycle, percent."

64 67 70 67 62 B1refringenee,An 0.0656 0.0673 0.0603 0.0649 0.1580

The yarn sample of this example which was afterstretched at a draw ratio of 1.5 as described above, was subsequently subjected to a hot wet treatment by immersing it in water at 250 F. and p.s.i.g. for minutes. The resulting yarn had a denier of 96, an initial modulus of 20 grams/denier, a tenacity of 1.6 grams/ denier, a breaking elongation of 53%, an elastic recovery after the first cycle as described above, of 91% and an elastic recovery after the 6th cycle of 50% extension as described above, of 82%.

EXAMPLES IX AND X The procedure of Example VIH was followed except that the spinneret contained 13 holes, each of which was 12 mils in diameter by 18 mils in length resulting in a shear ratio of 1600 reciprocal seconds, and the resulting yarn was taken up at a speed of 1000 feet/minute with a drawdown ratio of about 90 (Example IX) or at a speed of 1250 feet/min. with a drawdown ratio of 110. Properties of the resulting as spun yarns are shown in Table 6.

TABLE 6 Example Property IX X Denier 93 75 Initial modulus, grams/denier. 19. 4 26. 7 Tenacity, grams/denier 1. 06 1. 36 Breaking elongation, percent- 105 110 Elastic recovery from 50% extension at zero recovery time, percent 78 75.2 Birefringence, An 0. 0617 0. 0701 The following examples illustrate the use of quench temperatures, i.e. temperatures of circulating air in the spinning column downstream of the spinneret, of other than room temperature.

EXAMPLES XI AND XII The procedure of Example VIII was followed except that different conditions of quench temperature, takeup speed and drawdown ratio were used. These variations in the conditions of the process as well as the properties of the resulting as spun yarns are shown in Table 7.

The data in the above table illustrates that as spun yarn having relatively high elastic recovery may be produced using an elevated quench temperature.

The values of tenacity, breaking elongation, modulus, stress and strain given above were determined in a con- 10 ventional manner with the use of an Instron Tensile Tester operating at a strain rate of /minute. The initial modulus as the term is used above was determined by measuring the slope of the stress-strain curve at the point indicated by 1% strain.

The values of elastic recovery given above were also determined with the Instron at a strain rate of 100%/ minute. After the yarn was extended to the desired strain value, the jaws of the Instron were reversed at the same speed until the distance between them was the same as at the start of the test, i.e. the original gauge length. The jaws were again reversed, i.e., immediately for values of elastic recovery at zero recovery time, or after two minutes for values obtained at two minutes recovery time, and were stopped as soon as the stress began to increase from the zero point. The elastic recovery is then calculated as follows.

Measurements with the Instron at room temperature were carried out in air at 65% relative humidity. Determination at elevated temperatures were determined in air at 70 F. and 65% relative humidity which was heated to the desired temperature.

Values of birefringence were determined with a polarizing microscope equipped with a Berek compensation, in accordance with procedures well-known in the fiber arts. The value of birefringence is a measure of the degree of molecular anisotropy of the filament which in turn is indicative of the degree of molecular orientation produced as a result of spinning and drawing procedures.

Although the product and process of this invention have their most desirable embodiments in conjunction with random oxymethylene copolymers as pointed out above, oxymethylene homopolymers are also contemplated, e.g. as prepared by the polymerization. of anhydrous formaldehyde or by the polymerization of trioxane which is a cyclic trimer of formaldehyde. High molecular weight oxymethylene homopolymers as Well as random copoly mers may be prepared in high yields and at rapid reaction rates by the use of acidic boron fluoride-catalysts such as boron fluoride itself, and boron fluoride coordinate complexes with organic compounds, as described in US. Pats. 2,989,585; 2,989,506; 2,989,507; and 2,989,509 of Hudgin and Berardinelli, 2,989,510 of Bruni; and 2,989, 511 of Schnizer, as well as in the above-cited Pat. No. 3,027,352 of Walling et al.

In addition to the methods disclosed in the abovecited patents, other methods may be used to prepare oxymethylene copolymers and homopolymers contem plated under this invention, including those taught by Kern et al. in Angewandt Chemie 73 (6), pages 177 to 186 (Mar. 21, 1961), e.g. homopolymers in which the end groups have been reacted with an alkanoic acid such as acetic acid or an ether such as dimethyl ether. These reactants cause stable ester or ether end groups, e.g., acetyl or methoxy groups, to form at the ends of the polymer molecules. 7

The elastic filamentary materials of this invention are useful in a wide variety of applications. Because of the importance of these applications, they will be described in some detail below, under separate headings.

Replacement for wrapped core elastic yarns In many applications, rubber or so-called spandex fibers are employed as the core in a wrapped-core yarn construction, the wrapping being comprised generally of staple or filament yarns made of conventional high modulus low-stretch fibers such as cotton, rayon, nylon, etc. The process of wrapping is costly and frequently difficult to control. The properties of the wrapped yarn are somewhat unpredictable and often represent only a compromise between what is desired and what can be achieved by the combination of two or more yarns assembled and held together under radically different levels of strain.

For example, a typical double-wrapped spandex core, cotton wrapped yarn may be produced with the core pre-stretched 300400% when the wrapping is twisted around it. In the at rest state, the core retracts to some strain lower than that at which it was wrapped, thereby causing the wrapper yarns to be compressed into a jammed helix configuration.

Subsequent stretching of such a yarn, then, represents the combined effect of re-extending the core from some already partially stretched state and the opening of the jammed helix configuration of the wrapper. The stretch modulus of such a complex combination of material properties and geometric structure is easily disturbed by a number of transient variables in original manufacture and subsequent processing as well as during use of such yarns and fabrics made therefrom. Moreover, the ultimate stretch of such yarns cannot be varied independently of the stretch modulus.

The core-wrapper structure attempts to combine the virtues of high elastic recovery from high strain of the core with the relative rigidity of the wrapper. The principal object of such a combination is to achieve relatively high power of recovery from fairly high exten- The elastic yarns of this invention are very suitable for the replacement of such wrapped-core yarns for many applications. With a relatively high modulus obtained with the yarn of this invention, e.g., in the range of 2-15 grams/den, compared to spandex yarns with a modulus in the order of 0.2-0.5 grams/den, the yarn of the invention need not be pre-strained and wrapped in order to exhibit high stretch power. lUsed alone (i.e. without a wrapper) the yarn of the invention can provide substantial reduction in weight and bulk at the same level of stretch power, extensibility, and recovery. Thus, many fabrics may be markedly reduced in weight and bulk, made more sheer, by their use. On the other hand, at the same weight of yarn, density of weave, etc., fabrics produced from the yarn of the invention exhibit substantially more power than wrapped-core fabrics.

Used as a single-component yarn, therefore, the yarn of this invention may be substituted directly for wrappedcore yarns at considerable saving in cost and improvement in performance. A typical useful construction is a 3-ply yarn having a total denier of 750 comprised of 75 filaments. Each single yarn is twisted up to t.-p.i. and the ply construction backtwisted to yield a balanced yarn. One familiar with the art will recognize many variations of yarn denier, twist, ply construction, and denier per filament suitable for individual applications.

Replacement for bare spandex or fine denier stretch yarns Fine denier continuous filament yarns (30 up to 100 denier, for example) comprised of a thermosettable polymer (especially nylon) have found considerable application in lingerie and intimate garments. While those yarns have customarily been knitted (generally tricot) or woven for such fabrics as standard yarns, increasing interest is displayed in the use of stretch yarns made therefrom.

Stretch yarns of such thermosettable materials are produced by a number of techniques such as stuffer-box crimping, tWist-set-untwist, edge-crimping, etc. The stretch characteristic is imparted by building geometric distortability into the individual filaments of said yarns.

An alternative approach to the use of stretch nylon yarns has been dependent on the application of bare or lightly wrapped spandex yarns. Here the stretch and conformability, of course, depends upon the material extensibility of the fiber. Knitted or woven fabrics from such yarns, however, are generally rather limp and suffer from the relatively low degree of thermal stability of the typical spandex materials and their sensitivity to discoloration and fading in storage and use.

The desirable virtues of either the geometrically stretchy nylon stretch yarns, or the bare or lightly wrapped spandex yarns for lingerie where stretch and conformability are desired, may be achieved by the use of light denier yarns of this invention. A typical application of such yarns is 70 or 100 denier stretch fabric for ladies slips.

Variable porosity parachute canopy fabric Multifilament yarns of this invention which exhibit high elastic recovery from loads approaching 90% of ultimate rupture are eminently suitable for the fabrication of variable porosity fabrics. A fabric of this type possessing approximately the following properties may be made from the yarn of this invention:

Weight 1-2 ounces per square yard Permeability of 50-90 cubic feet per minute per square foot at 0.5 inches of water pressure differential Ultimate tensile strength of 20 pounds per inch of fabric width in both warp and filling directions An exceptionally large permeability at a pressure differential that imposes a fabric tensile load of 15 pounds per inch of fabric width.

Atypical fabric construction having these properties is as follows:

Fabric specifications:

Weight: 2 ounces per square yd.

Ends per inch: 130

End denier: 60

Picks per inch: 130

Pick denier: 60

No. of fils per yarn: 21

Percent crimp filling: 6

Strip tensile warp: 20 lbs/inch of Width Strip tensile filling: 20 lbs/inch of width Ultimate elongation warp:

Ultimate elongation filling: 75

Yarn properties:

Yarn denier: 130

No. of filaments: 21

Ultimate stress: l.52.0

Ultimate elongation: 75%

Stress at 20%: 1.0 g.p.d.

Elastic recovery at 20% strain: 99%

Elastic recovery at 50% strain: -90% Fabric performance:

Porosity at low strains: 50-90 cubic feet per minute per square foot at 0.5 inches of water pressure differential Porosity at a stress of 5 pounds per inch of fabric 'width: 1000 cubic feet per minute per square foot at 4.0 inches of water.

Woven foundation garments, elastic bandages, and like products Candidate fabrics for woven foundation garments, elastic bandages and similar products comprise anywhere from 5 to elastic fiber content in fabric weights from 2 to 15 ounces per square yard. Highly recoverable stretch with presently available materials is possible from strain levels of 20 to 40%.

By employing the filamentary material of this invention, it is possible to obtain durable elastic recovery from higher strain levels than presently available with spandex and rubber materials and greater range of available power at given strain levels.

A typical woven batiste foundation fabric is as follows:

Fabric weight: 4 ounces per sq. yd. Warp-acetate: denier Ends per inch: 65

Fillingyarn of this invention: 200 denier Picks per inch: 60

Elastic recovery at 60% strain: 95%

Stretch level: 50%

Rupture tenacity warp: 45 lbs. per inch of width Rupture tenacity filling: 40 lbs. per inch of width Modulus in pounds at 40% strain: 10 lbs. per inch of width Other stretch fabrics also rely upon the incorporation of bulked/stretch yarns or spandex-type yarns in combination with other less extensible yarns. The elastically recoverable yarns in some of these fabrics comprises, for example, from to 65% of the fabric which performs elastically up to strain levels of 100% in the elastic direction.

A typical ski pant fa'bric utilizing the material of this invention contains 150 ends per inch of 70 denier, 21 filament yarn of this invention and 42 picks per inch of 700 denier, 2 fold worsted yarn, and has a plain weave construction.

Stretch linings The advent of stretch apparel has created a necessary demand for stretchable lining fabrics. These materials should be lustrous and consequently spandex and textured constructions are generally unsuitable. The highly elastic lustrous multifilament yarn of this invention is, however, very suitable for conversion into Woven stretch linings.

A typical example of a suit lining fabric contains 100 ends per inch of 150 denier acetate having 120 filaments per yarn, and 64 picks per inch of 140 denier yarn of this invention having 40 filaments per yarn in a 2/1 twill weave having a fabric weight of 3 ounces per square yard.

Wire wrapper Wires intended for use in electrical circuits are often Wrapped with a single or double layer of textile yarn as a means of insulating them from adjacent conducting elements. The yarn of this invention has characteristics which make it particularly suitable for such an application. Its stretchability ensures a tight wrap which is particularly resistant to opening due to abrasion, and its high dielectric strength ensures adequate insulation at minimal weight of wrapping yarn.

Wrapped spandex yarn Yarns which are made by wrapping spandex yarn with one or two layers of a conventional yarn have load-elongation curves which are characterized by a low modulus initially, and a very high modulus when the covering yarns become stretched. This abrupt large change in modus is often undesirable, and can be avoided by using the filamentary material of this invention as the covering yarn. By varying the angle of wrap of such yarn, modulus values, extending over a range of extension of significantly more than 100%, can be varied from those typical of spandex up to those typical of the yarns of this invention and the magnitude of any changes in modulus with extension can be reduced greatly from those resulting from the use of conventional fibers in the wrapping yarn.

Blends with other fibers Spun stretch yarns composed predominantly of conventional fibers such as cotton, wool, nylon, polyester, or other commonly-used materials, can be produced by blending such fibers with 5 to 45% of staple fiber of this invention. Such blending is carried out in a card, gill-box, pin-drafter, Pacific Converter, or other normally-used blending procedure prior to spinning the yarn. The relatively high modulus of the fiber of this invention makes these blending operations much easier to control than when other elastic fibers having a much lower modulus are used, and drafting and spinning is accomplished with only minor adjustments of normal machine settings. The final product can be used to produce fabrics having usable stretches in the range of to 30%, and the high recover- 14 ability and high recovery energy provided by the filamenrtary material of this invention ensures excellent elastic characteristics in the stretch fabric, and minimizes or eliminates the problem of pilling encountered with lowmodulus fibers.

Bulk stretch yarns Bulked yarns as presently being produced are characterized by being lofty, but not having unusual stretch characteristics. Stretch yarns, on the other hand, may be bulky, but they achieve their stretchiness at the expense of reducing this bulk; that is, by removal of the crimp which causes it. A true bulk stretch yarn would be one in which the bulk is retained when the yarn is stretched. This could be accomplished if the fibers from which the yarn was made had a low enough modulus to ensure that the yarn could stretch by virtue of the fibers themselves stretching, and not primarily or exclusively by a crimpremoval mechanism.

Yarns made from the fibers of this invention can be made bulky by drawing them under slight tension over a sharp, unheated edge, followed by stretching and relaxing. This causes the filaments to kink extensively, and results in a very bulky yarn having 50 to of highly recoverable stretch. Such bulky stretch yarns are useful for producing light, lofty fabrics, in the range of 3 to 10 ounces per square yarn, having excellent cover and the ability to recover their original dimensions after being stretched 50% or more. Moreover, much of this bulk is retained over wide ranges of stretch, and thus the fabric cover is not seriously reduced by stretching, making it ideal for applications like bathing suits, form-fitting blouses, leotards or other form-fitting garments, etc.

Fabrics for these applications can be made somewhat more open from the yarns of this invention than from other types of stretch yarns, thus providing the possibility of constructing lighter, more porous and, therefore, more comfortable fabrics.

Stretch sewing threads One of the current problems in the production of garments made from stretch fabrics is to retain that stretch in the seam of these garments. This can easily be accomplished by using a sewing thread which is capable of stretching with the fabric. The sewing thread, on the other hand, must be capable of withstanding the normal stresses imposed by the sewing operation without undue stretch, or seam puckers will result. Sewing threads having the desired characteristic of good sewability and capable of providing the stretch needed in the seams of garments made from stretch fabrics can be made from fiber of this invention in a number of ways. One such thread can be produced in normal sewing thread constructions using the filaments of this invention in place of those made from other fibers. A gradation of stretchability can be provided by producing yarns from blends of staple fiber made from the filaments of this invention in varying amounts with cotton, nylon, or other textile fiber, and using such yarns in conventional sewing thread constructions. Still another siutable yarn "for the production of stretchable sewing threads is one in which normal textile fibers are either spun or wrapped around a yarn of this invention as core, in any one of a number of normal core yarn manufacturing techniques.

Bulk filling material Pillows and cushions are generally filled with synthetic or natural fibers to produce a resilient end product. Certain fibrous materials, due to poor elastic recovery from bending and a tendency to cluster or clump, demonstrate poor durability as pillow or cushion fillers. A cut staple fiber such as that made from the filamentary material of this invention, crimped and/ or bulked, has very desirable properties as a filling material. A typical blend for filling pillows made completely from filamentary material of this invention is as follows:

50% low modulus: 6 denier material 50% medium modulus: 3 denier material Staple length: 3 inches Crimps per inch of fiber length:

Stretch nonwovens Nonwoven fabrics are relatively stilf materials which do not drape or conform to bodily contours as do normally woven fabrics. A method of improving the quality of a nonwoven fabric in terms of drapeability and recoverability from imposed strains is to construct the nonwoven in par-t or entirely from fibers of this invention. The highly elastic nature of relatively low modulus fibers of this invention in low deniers can make them desirable materials for stretch nonwovens.

A typical nonwoven is composed of 1 /2" cut staple, low modulus fibers made from 3 denier filaments of this invention and having a web weight of 2.0 ounces per square yard and a 30% by weight low modulus high strength adhesive binder.

.Tufted carpets A typical application, taking advantage of the recovery properties of the material of this invention is in a rug backing (either in total or as a component) for tufted carpets. A tightly woven fabric of suitable construction and weight passes through the tufting machines under filling-wise extension and tension (approximately 25% extension). The base fabric is tufted in this form after which the filling tension is allowed to relax. The fabric then contracts, which causes the pile to condense producing a heavier and denser pile than can currently be obtained by the present rug backing fabrics (jute, cotton, polypropylene). This procedure produces carpets with a denser pile, and therefore with a more enhanced and more luxurious-looking pile than can currently be produced by prior art methods. Besides the advantage of appearance, the more compact pile has better resistance to crushing, better abrasion properties, and longer wear, etc.

A typical construction of such a rug backing fabric is a plain woven fabric weighing about nine ounces per square yard constructed from 3100 denier yarns having a yarn count of 12.5 ends per inch by 13 picks per inch. These yarns can be either continuous filament or spun staple yarns.

Woven carpets The filamentary material of this invention has applications in the woven carpet industry as binding yarns in carpets. The high recovery forces of the yarn and fiber imparts higherand therefore more desirablebinding forces to the pile than can be obtained from current binding yarns. The higher binding forces also prevent pile pull-out and produce a more stable pile and carpet.

The additional case of extension of the yarn, with high recovery, also aids in the form fitting and stability of rugs on stairs, over angles, and around objects. In this application it applies to both the binding yarns and to the rug pads used underneath rugs.

The fiber is used in both spun staple yarns or continuous filament yarns in yarn number and construction currently used by the rug industry.

Form-fit fabrics: bed sheets, shirt collars and like products A typical application of the filamentary material of this invention which takes advantage of the high recovery force of the fiber is in the area of form-fit fabrics such as bed sheets and shirt collars. The advantage of such material in form-fit bed sheets over conventional form-fit sheets is that the higher retractive forces cause the form-fit sheets to adhere more closely to the mattress 16 producing a neater appearance and a more stable sheet than currently available form-fit sheets.

A typical woven sheeting construction utilizing the material of this invention in either continuous filament or staple spun yarns has a fabric width of 40 inches, a fabric weight of 4 yarns/lb. (3.3 oz./sq.yd.) and a yarn count of 48 warp ends per inch and 48 filling ends per inch.

The same advantages hold true for other form-fit applications such as shirt collars. These applications utilize either woven or non-Woven fabrics containing the material.

Glove fabrics 'Another typical application for the material of this invention, taking advantage of its high recovery and bulking ability properties, is in glove wear fa'bricsincluding woven, knitted, and nonwoven. The advantages of using such material are better bulking characteristics and better extensibility and recovery performance, and the resulting fabrics produce better warmth, better comfort, and more efiicient use. The ease of extensibility with high recovery results in more efficient and comfortable gloves than currently in use.

:The material may be used in the production of a wide range of glove products, from work gloves to women's fashion gloves.

Umbrella fabric A more compact folded umbrella may be made using fabric made from the yarn of this invention, having the ability to stretch 25% or more when the umbrella is opened, without serious loss of cover. This can be accomplished by using a high bulk yarn, so that even after the fabric is stretched, the yarn still retains sufiicient bulk to fill the fabric interstices and retain the required water repellency. The amount of bulk required varies with the amount of stretch desired, and the construction is adjusted to provide the prime requirement of high cover to provide good water repellency when the umbrella is open (i.e., when the fabric is stretched).

Novelty puckered fabric The material of this invention is suitable for a seersucker-type fabric in which bands of puckers run lengthwise in the fabric, and are of a size and frequency controlled by the fabric construction. These are produced by setting up a warp containing alternating bands of yarns made of any normal textile fiber and of the elastic yarns of the invention.

The latter yarns are wound onto the warp beam under tension sufiicient to stretch them 5 or more percent, and this stretch is maintained in the loom by adequate warp tensioning. After weaving, the fabric is permitted to relax, and the high energy of recovery provided by the yarns of the invention causes the whole fabric to contract, and in turn causes the surface to pucker in those bands which contain normal warp yarns. The advantage of yarns of the invention in such applications results from its high recovery energy. This permits both very light and very heavy fabrics to be produced more successfully than is possible by currently-used procedures.

Camp cot fabric The filamentary material of the invention is suitable for use in camp cot fabric for both military and civilian applications. The purpose of such material is to provide a small amount of recoverable stretch and thereby provide more comfort in use than is currently obtained from present camp cots. The material is suitable for use in all current camp cot fabrics, in plain weave, twills and other constructions.

A typical construction for this fabric contains 96 ends per inch by 64 picks per inch in a 40-inch width producing a fabric weighing about 2.5 yarns per pound (5.8 ounces per square yard).

Upholstery fabrics: outdoor and indoor The filamentary material of the invention is suitable for use in both outdoor and indoor upholstery fabrics. Such material imparts better drape, elastic, and formability properties to these fabrics than they currently exhibit. The case of extensibility with high recoverability enables easier, more elficient fabrication of the fabric to the furniture as well as producing a neater appearance after fabrication caused by the high recovery giving a tight or snug fit on the padding and structure of the upholstery.

Current upholstery fabrics come in a wide range of types, weights, and construction. The material of the invention may be used, Without restrictions, in all types of such fabric either as part of a blend or alone. The material may be in either staple form or in continuous filament form depending upon the desired end characteristics.

Shoe applications: fabric and linings The filamentary material of the invention finds many applications in the shoe industry in both outer shoe and sneaker fabrics as well as inner shoe linings. In use, many shoe fabrics fail in the area of fabrication to the leather. Because of the relative ease of extensibility of the material of the invention, associated with high recoverability, the shoe fabric containing such material can be fabricated to the shoe with less internal stress. Also, during walkingapplicable to both shoes and sneakersthe fabric extends easier and recovers more completely thereby producing a more comfortable and longer-lasting shoe or sneaker. The lower stresses on the elastic material where the fabric covers the toes results in more comfortable and longerlasting sneakers.

The ease with which fabrics comprising the filamentary material of the invention can be formed and coated or impregnated make it very desirable for shoe linings. Such fabrics adhere to the shape of the shoe easily, without wrinkles, and lend themselves easily to stitching and fab rication of the shoe.

The material is utilized in all presently used shoe fabricand shoe lining fabric constructions. It can be used in the form of spun staple yarns or continuous filament yarns and may comprise one hundred percent of the fabric or a component part of the fabric.

Coated fabrics The material of this invention is useful in the manufacture of highly elastic coated structures. As is well known to coaters, soft, drapey, elastic coated fabrics can be made utilizing cotton knit goods as contrasted with typical woven cotton sheetings and twills due to the stretchability of knit fabrics. This stretcha'bility is translated to the coated structure and is useful in formable furniture and automatic upholstery, headlining or for leatherette, as it is known, which is also used for luggage, etc.

In coating knitted fabrics with vinyl compositions or other plastic films by coating or lamination, it is generally noted that knit fabrics require more coating materials to fill the interstices and to obtain level, smooth coatings as compared to those same coatings on flat woven structures.

Woven fabrics containing the material of the invention exhibit stretch characteristics of the knit fabrics while enjoying the benefits of coating virtues of flat woven structures. 'Better overall reinforcement of plastic films also results from compatible characteristics of stretch of both the yarn and the plastic film to make better performing products.

Fabrics containing the elastic material of the invention can be constructed of either filament or spun yarns as desired and made in roughly comparable weight and strength with typical constructions of other fibers now used, as for example the woven sheetings of cotton such as the 80 x 80 print cloth of 4 sq. yds. per pound or heavier sheeting of coarse yarns as a typical 48 x 48 construction of 2.6 sq. yds. per pound. Weights and weaves like typical canvas or special weaves as twills and drills are likewise of use.

To gain extreme extensibility for special uses the material may be knit into fabrics of structure similar in weight and strength to cotton knit goods. The stretch of the yarns of the invention added to that already available from the knit structure yields coated structures of unusual softness, pliability, and elasticity. This enables the coater to produce structures that can be made to conform to odd shapes and around corners without producing unsightly folds or damage to the base fabric.

Coated fabrics using heavy fabrics comprising the elastic material of the invention are highly desirable in coated inflatable or air supported fabrics. The easy extensibility and high recoverability of this fiber make it easy to fabricate and give a neater appearance at the seams while under air pressure. The fabric adjusts itself easier to changes in air pressure under use because of the extensibility and recovery properties.

Nets

Nets are extremely open structures formed by knotting together the component yarns at the intersections. They are extremely deformable structures because of the rela tive infrequency of the points of restriction created by the knots. They have little if any tendency to recover from any deformation. A significant amount of recovery could be provided by making the nets out of yarns of this invention, which, because of their ability to stretch and high energy of recovery, make it possible to produce nets with a characteristic not provided by normal net constructions. Thus, form-fitting hairnets, useful over a Wide'range of head sizes, are contemplated from yarns of the invention of denier or less. Expandable containers (e.g. laundry bags) and carrying bags are easily produced from heavier yarns, in the range of 100 to 1000 denier or more. Also, gill nets are contemplated which are designed to catch a wider range of fish size than do those made from from conventional fibers, in which the larger fish are lost because they cannot get their heads through the mesh. These contain cords of more than 1000 denier.

Support hosiery Whereas the majority of support hose utilize relatively coarse yarn constructions to create the necessary amount of support stress at a Worn strain (anywhere from 0 to 2 pounds per inch of fabric width depending upon leg size, position on the leg and amount of support required) it is possible to utilize yarns of this invention to produce, in combination with other materials, a much shearer sup port hose.

One technique whereby elastic filaments are utilized is by laying in continuous filament elastic yarn within the knit loops of the stocking. Using the filament yarn of the invention, a typical construction for a support stocking is as follows:

Wales per inch: 30 to 60 Courses per inch: 30 to 65 Knit structure: 30 denier nylon monofilament with 35 denier filament of the invention laid into the knitted mesh It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A melt spun oxymethylene polymer filamentary material having at 70 F. an elastic recovery of at least about 70 percent from an extension up to about 50 percent, said filamentary material being a copolymer of trioxane with from about 0.5 to 25 mole percent of an oxygen containing cyclic ether having adjacent carbon atoms and a ring size of 3-7 members, said filamentary material having been spun at a shear rate of from about 250 to 2,500 reciprocal seconds and subjected to a drawdown ratio of from about 25:1 to 350: 1, an after-stretching operation at a temperature of from about 50 degrees Fahrenheit to 250 degrees Fahrenheit and a draw ratio of no greater than about 2.3: l, and a second after-stretching operation by contacting said filamentary material with hot H O at a temperature of from about 190 degrees Fahrenheit to 250 degrees Fahrenheit for at least one minute at a draw ratio of no greater than about 2.3: l.

2. The random oxymethylene copolymer filamentary material of claim 1 having at 70 R, an elastic recovery at zero recovery time of at least about 75 percent from an extension of 50 percent, a breaking tenacity of at least about 1.0 gram/denier, a breaking elongation'of at least about 55 percent, an initial modulus of at least about 2 grams/denier, and a birefringence of at least about 0.03.

3. The random oxymethylene copolymer filamentary material of claim 1 having at 70 R, an elastic recovery at zero recovery time of at least about 80 percent from an extension of 50 percent, a breaking tenacity of at least about 1.3 grams/ denier, a breaking elongation of at least about 75 percent, an initial modulus of at least about 5 grams/denier and a birefringence of at least about 0.05.

4. The product of claim 1 having an elastic recovery at 7 References Cited UNITED STATES PATENTS 2,768,994 10/1956 MacDonald 26067 FP 2,844,561 7/ 1958 Bechtold et al. 260-67 FP X 3,134,636 5/1964 Singleton 260-67 FP X 3,231,543 l/1966 Jamison 260-67 FP X 3,330,897 7/ 1967 Tessier 26067 FP X 3,347,969 10/ 1967 Moelter 260-67 FP X 3,479,314 11/ 1969 Williams 26067 FP X WILLIAM H. SHORT, Primary Examiner L. M. PHYNES, Assistant Examiner US. Cl. X.R. 2642l0 

